The present invention relates to encoding and compression for transmitting and recording super-audio signals having a quality of reproduced sound much higher than that of compact disk.
There are a variety of techniques for compression of audio signals. Two major techniques are known. One of them is a lossless compression where redundant data which depend on self-correlation or relative-correlation of the data of music signals are extracted, and only the redundant components are compressed for transmission and recording. The other is perceptual encoding where dull components are allowed to be deleted based on the ambiguity of the human audible properties to perform a high efficiency of the encoding (or the quality is degraded). The latter is commonly used together with the former for low bit rate communication and package media. However, it is essential in the super-audio technology for targeting a much higher level of the sound quality than the compact disk (hereinafter referred to as CD) technology to employ the lossless compression which does not cause degradation of the quality. The following description is hence limited to the lossless compression.
One of such conventional techniques is disclosed in xe2x80x9cSerial transmission apparatus with data compression functionxe2x80x9d in Japanese Patent laid-open Publication 7-74675(1995). The object thereof is to improve the transmission rate in a serial transmission apparatus. An output of an analog-to-digital converter which converts. input analog signal to digital signal is processed by a differential process, and the signals are compressed by the Huffman conversion. As the high-rate data is compressed and transmitted over a line having a given communication speed, the substantial transmission rate is increased, and this prior art is similar to the present invention on this point. The differential process functions to bias the profile of appearance probability of digital data, and this improves the compression efficiency in the Huffman conversion at the later stage. In other words, the differential circuit can increase its advantage by cooperating with the Huffman conversion circuit. For example, it is said that the compression rate for converting audio data directly by the Huffman compression is generally 90 to 95%, and similar data have been confirmed through a series of experiments by the inventors. When the Huffman compression is performed after the differential process, the rate may slightly be increased to 85 to 90%.
Meanwhile, as a variety of high-density recording media including DVD have been developed so far, the pulse code modulation (PCM) super-audio technology can be realized in a wider frequency range and in a wider dynamic range. The DVD audio technology is just on the stage of standardizing its format. Its draft version, Book 0.9, was explained in a meeting at Tokyo on Apr. 21, 1998. One of publications that introduces the meeting is xe2x80x9cRadio Technologyxe2x80x9d, June 1998, Vol. 52, No. 6, Serial No. 695, by IA Publishing, pp. 73-77. According to the report, the major parameters of the DVD audio technology include sampling frequencies of 48 kHz/96 kHz/192 kHz and 44.1 kHz/88.2 kHz/176.4 kHz, number of linear PCM quantization bits of 16/20/24, and maximum number of channels (ch) of 6. It is to be noted that the maximum bit rate is set to 9.6 Mbps. Any combination of the above parameters can be accepted as far as the bit rate is not greater than the determined level. For instance, a combination of 96 kHz, 24 bits, and 4 ch has bit rate of 9.216 Mbps, and it can be utilized. However, another combination of 96 kHz, 24 bits, and 5 ch has bit rate of 11.52 Mbpts which exceeds 9.6 Mbps, and it cannot be used. A further combination of 96 kHz, 24 bits, and 6 ch has bit rate of 13.824 Mbps exceeding 9.6 Mbps, and it cannot be used.
As to the movie, multi-channel systems becomes popular particularly in the United States of America. Some of home appliances employ multi-channel systems such as 5.1 channel (three channels at front center, left, and right, two channels at rear left and right, and one channel for a subwoofer), and others may follow before long. In view of such a background, a multi-channel system is also desired to employ the super-audio format. It is known that a combination of 96 kHz, 24 bits, and 6 ch is feasible with the use of high performance recording equipments available. It is then proposed to transmit and record DVD audio signals without degradation. Hence, the DVD audio technique is now demanded for the application of 96 kHz, 24 bits, and 6 ch.
In addition, besides the application of 96 kHz, 24 bits, and 6 ch to the DVD audio system, the recording time of 74 minutes on a single recording side is also desired, similarly to CD. This resides on the facts that most music workpieces are finished within 74 minutes and that master sources produced in the music industry are designated to fall in the length of 74 minutes. If its playback period stays within 74 minutes, both of the CD and DVD can favorably be planned, manufactured, and marketed. It is hence crucial for storage on a given size of disk medium that 4.7 GB (gigabytes) data in the DVD format are compressed so that its bit rate calculated by dividing 4.7 GB with the playback period (74 minutes) is not higher than 8.47 Mbps.
The foregoing requirements are now compiles below.
(a) The data compression shall be conducted by lossless compression which permits reversible conversion.
(b) The transmission rate shall be not higher than 9.6 Mbps defined as the maximum level in the DVD audio format.
(c) The average transmission rate shall be not higher than 8.47 Mbps for not exceeding the playback time of 74 minutes.
(d) Preferably, the data shall be compressed to 60% or less for allowing the playback time of 74 minutes at the mode of 96 kHz, 24 bits, and 6 ch.
The invention is developed to achieve the above requirements, and its object is to provide a method and an apparatus for carrying outlossless compression encoding and decoding of data (a) in a perfectly reversible mode, (b) at a peak transmission rate of not higher than 9.6 Mbps, (c) at average transmission rate of not higher than 8.47 Mbps or playback time of 74 minutes, and (d) at compression ate of 60% or less when playback time of 74 minutes is attained in the format of 96 kHz, 24 bits, and 6 ch.
In a method and in an apparatus for lossless compression encoding according to the invention, a given number of input data samples in a predetermined length of time is grouped to blocks, correlation between the samples in each block is deleted, redundant run lengths are determined in the data after subjected to the correlation deletion, and minimum of the redundant run length or run length of a common redundant portion in the samples is detected. Then, the common redundant portion is deleted from each sample, the data which have been subjected to the deleting the common redundant portion are subjected to the Huffman conversion, and the run length data of the common redundant portion and the Huffman-converted data for each sample are provided.
In a method and in a apparatus for lossless compression decoding according to the invention, code data are received which comprises run length data of a common redundant portion and data subjected to Huffman conversion in each sample, the data having been obtained by the steps of grouping a given number of input data samples in a predetermined length of time to blocks, deleting correlation between the samples in each block, determining redundant run length or run length of a common redundant portion in the samples after the correlation deletion, and deleting the redundant run length from each sample. Then, a conversion algorithm is get from the input data, and it is used for the Huffman decoding, and the run length data of the common redundant portion is gotten and added to the decoded data after the Huffman decoding. Then, correlation decoding is performed on the data to which the redundant portion is added.
Thus, in the method and the apparatus for lossless compression encoding, the redundant portion is deleted by using correlation in the input signals, and the signals are further compressed efficiently; with use of bias in the data profile. Thus, the data is reduced to a size substantially equal to the entropy of the input signals. Further, in the method and the apparatus for lossless decoding, the compressed data are decoded in the reverse sequence. Thus, the input signals of audio signals of a wide-band multi-channel format can be reproduced completely without degradation. As a result, the method and apparatus for lossless compression encoding or decoding can be provided where complete lossless compression is realized and the amount of data to be transmitted can be reduced to 60% or less.
In the method and the apparatus of lossless compression encoding, in the deletion of correlation, a difference, or a predictive difference, between the data predicted by a predictor or a predictive filter and the real data is taken out. For example, the predictor or the predictive filter comprises a circuit for integer calculation having accuracy equal to a range of integers of the input data.
Further, in the method and the apparatus of lossless compression encoding, in the Huffman conversion, the data after deleting the common redundant portion are separated to an upper part having a predetermined number of bits and a lower part of the other bits, and only the upper part is subjected to the Huffman conversion. In the method and the apparatus of lossless compression decoding, in the Huffman decoding, the input data are separated to an upper part in correspondence to a given pattern of the Huffman conversion and a lower part having a predetermined number of bits determined by the data transmitted as a parameter for each block, and only the upper part is subjected to the Huffman decoding.
The apparatus of lossless compression encoding comprises a plurality of sets of the above-mentioned correlation deleter, common redundant bits deleter and Huffman conversion device. Further a maximum efficiency data output device is provided to select and output data which provide maximum efficiency from the output data of the plurality of the Huffman conversion devices. It outputs a combination of the data which provides the maximum efficiency and transmits a parameter indicative of the combination.
In the method and the apparatus of lossless compression and encoding or decoding, the most advantageous is selected among a plurality of correlation deletion characteristics.
In the apparatus of lossless compression encoding, a plurality of correlation deleters are provided to delete correlation. Output data of each of the correlation deleters are subjected to the deletion of the common redundant portion, and each data after the deletion of the common redundant portion is subjected to the Huffman conversion. Then, a combination having the maximum efficiency is selected among the data subjected to the Huffman conversion, and a parameter indicative of the combination is transmitted.
In the method and the apparatus of lossless compression encoding, the Huffman conversion is performed by selecting and using one of conversion algorithms which provides the maximum efficiency for the block, and a parameter indicative of the algorithm is transmitted.
In the method and apparatus of lossless compression data decoding, in the correlation decoding, a sum of a predictive data generated by the local predictor or the local predictive filter and the transmitted input data is taken out. The local predictor or the local predictive filter comprises, for example, a circuit for integer calculation operated at accuracy equal to that of a range of integers of playback data.
In the method and the apparatus for lossless compression decoding, in the Huffman decoding, a signal is selected having a property determined by the data transmitted for each block.
The apparatus for lossless compression decoding further comprises an associate data detector which detects an associate data associated with the received coded data. The Huffman decoder includes a plurality of Huffman tables, and the associate data detector selects one of the Huffman tables corresponding to the associate data.
In the method and the apparatus for lossless compression decoding, sample data positioned at a particular position in the top of each block are linear pulse code modulation data. Thus, the speed to return from error propagation can be increased, and reproduced sound of special mode of cue/review can be heard with ease.
A recording apparatus may comprise the above-mentioned lossless compression encoding apparatus and a DVD formatter which converts the signals received from the lossless compression encoding apparatus to DVD format signals, and the like.
A playback apparatus may comprise the above-mentioned lossless compression decoder, a DVD de-formatter which converts the signals to code data, and the like.
An advantage of the method and apparatus for lossless compression encoding and decoding according to the present invention is that a large volume of data can be compressed without degradation thus for recording and play-backing more information throughout a longer time.